(1) Field of the Invention
This invention relates to a novel method of cleaning integrated circuit wafer after metal etch. After metal etch residual chlorine ions which are not completely removed during wafer cleaning can combine with water and cause metal corrosion. This invention provides a method to passivate the chlorine ions before wafer cleaning by converting them to a stable polymer. The chlorine is then stripped off during the photoresist cycle and a wet organic cleaning cycle.
(2) Description of the Related Art
Conventional processing of integrated circuit wafers requires metal etch with a chlorine species etchant. The photoresist is then stripped using a CF.sub.4 and O.sub.2 plasma followed by an O.sub.2 strip and a water rinse. At a low percent CF.sub.4 this method will not convert all available chlorine ions to fluorine ions leaving residual chlorine ions. When the residual chlorine ions contact water during the water rinse they will cause corrosion of the metal electrodes. At a high percent CF.sub.4 the CF.sub.4 /O.sub.2 mixture will etch the barrier metal causing undercutting and a metal lifting problem. Wet organic cleaning is very effective in removing chlorine ions and polymers but the chlorine level must be low enough so that the water rinse will not cause corrosion pits, often called mousebites during the rinse step. The corrosion can also proceed slowly and lead to a serious reliability problem.
Adequate cleaning of integrated circuit wafers after intermediate and final process steps is of great importance in semiconductor processing. U.S. Pat. No. 4,962,049 to Chang et al uses plasma oxygen to remove impurities, such as moisture, occluded gases, etc. from the wafer. This patent is particularly concerned with the back side of the wafer. Residual chlorine has long been recognized as a key problem in wafer cleaning due to the corrosive nature of chlorine in the presence of moisture.